1. Field of the Invention
The present invention relates to a coating die for coating a coating liquid simultaneously on the two sides of a band-shaped base material moving in longitudinal direction. The invention also relates to a coating die capable of forming an intermittent coating layer on the two sides of a base material.
2. Description of the Related Art
A coating die for coating a coating liquid simultaneously on the two sides of a band-shaped base material is disclosed in JP-A-51-137760. This conventional coating die, as shown in FIG. 1, is an apparatus for coating the two sides of an aluminum foil 1 and bonding paper 3 to one of the coating surfaces to produce a cover of the cup for the cup noodle.
When the aluminum 1 is sent out to a pair of cooling rolls 5, a coating hot melt 9 is supplied from a T-die 7, and hot and molten polyethylene or the like molten resin 13 is supplied from a T-die 11. These coating materials are applied to the two sides of the aluminum foil 1, and the paper 3 supplied to the cooling rolls 5 adheres to one side of the aluminum foil 1 through the molten resin, thereby producing a product.
A spacing 15 is formed between the T-dies 7, 11. The air involved when the aluminum foil 1 passes through the spacing 15 is absorbed by fans 17 and discharged outside through pipes 19. The bonding failure of the coating resin thus is prevented. The thickness of the aluminum foil and the hot melt layer is adjusted by moving regulation plates 21 with respect to the aluminum foil 1.
This conventional coating die, although capable of coating the two sides at the same time, has the disadvantage described below since the the hot melt 9 and the molten resin 13 constituting the coating liquid are brought into contact with the aluminum foil 1 constituting the base material in the atmosphere.
(1) The coating liquid is liable to oxidize or otherwise degenerate in contact with the atmosphere before coming into contact with the base material.
(2) The coating pressure is nil and the coating is effected in an open environment. The coating strength is therefore difficult to improve, resulting in a low adherence of the coating film. Especially in the case where a porous, perforated or grooved base material is used, the coating liquid finds its way into the spacing of the base material difficult, thereby making it difficult to improve the production speed.
Another coating die of this type disclosed in JP-A-1-194265 is used for forming an intermittent coating layer on the two sides of a base material sheet in the process for manufacturing the electrode plates of a lithium-manganese secondary cell.
A coating die 300, as shown in FIG. 2, supplies a base material sheet 304 of an aluminum foil from a supply unit 303 with a coating material 302 held in a storage section 301. When the base material sheet 304 is moved along the direction of arrow, shutter members 305, 305 are slid in the direction of X (the position shown in FIG. 2) and then kept stationary for a predetermined length of time. Then, the shutter members 305, 305 are slid in the direction of Y until they come into contact with doctor blades 306, 306, and then kept stationary there for a predetermined length of time. These series of operation are repeated in cycles.
In FIG. 2, reference numeral 307 designates guide members, numeral 308 a dryer, numeral 309 a take-up unit and numeral 310 a turn roller.
With the shutter members 305 slid along the direction of X, the shutter members 305 and the doctor blades 306 are separated from each other, and the coating material 302 from the storage section 302 is coated simultaneously on the two sides of the base material sheet 304. Further, the coating material 302 is scraped off by the doctor blades 306, so that the coating material 302 is coated in a predetermined thickness on each of the two sides of the base material sheet 304.
With the shutter members 305 slid along the direction of Y, on the other hand, the shutter members 305 come into contact with the doctor blades 306, and the coating material 302 is prevented from being supplied from the storage section 301 to the base material sheet 304. Therefore, the coating material 302 is not coated on the base material sheet 304.
As a consequence, in the coating die 300, the base material 304 is moved while the shutter members 305 repeatedly slide along the directions X and Y. It is thus possible to form an intermittent coating layer of the coating material 302 simultaneously and continuously on the two sides of the base material.
Another method of forming an intermittent coating layer is shown FIG. 3.
In this method of forming an intermittent coating layer, an intermittent coating layer of the coating material 302 is coated on the base material sheet 304, one side at a time.
More specifically, a coating die 400 coupled through a transport pipe 321 to a storage section 301 of a coating material 302 is controlled to come into and out of contact with a running base material sheet 304 in accordance with a coating pattern of an intermittent coating layer to be formed. With the approach of the coating die 400 to the base material sheet 304, a coating layer 320 is formed on one side of the base material sheet 304 (FIG. 3A), while a non-coated portion 322 is formed as the coating die 400 comes away from the base material sheet 304 (FIG. 3B). The repetitive cycles of the coating die 400 coming into and out of contact with the base material sheet 304 causes an intermittent coating layer of a desired pattern to be formed on one side of the base material sheet 304. In the process, the coating die 400 supplies the coating material 302 with the approach thereof to the base material sheet 304, while the supply of the coating material 302 is stopped as the coating die 400 comes away from the base material sheet 304. The intermittent coating layer is formed, one side of the base material sheet 304 at a time, by the coating die 400, and hence an intermittent coating layer of the desired coating pattern can be formed on the two sides after all.
Nevertheless, the conventional coating dies 300, 400 have the disadvantages described below.
First, in the coating die 300, with the storage section 301 in open structure, the coating material 302 is liable to degenerate due to oxidization or the like phenomenon before coming into contact with the base material sheet 304. Also, since the coating pressure is zero, the bonding strength of the coating layer cannot be improved, resulting in a deteriorated quality of the coating layer.
With the coating die 300, the shutter members 305 are required to be opened and closed frequently depending on the coating pattern of the intermittent coating layer. The resulting liquid level variations of the coating material 302 is liable to change the thickness of the coating layer. Employing an immersion process allowing the coating material 302 to attach to the base material sheet 304 in natural way, this conventional method has the problem of a deteriorated uniformity and a low surface smoothness of the coating layer, resulting in a film thickness accuracy.
The coating die 400, on the other hand, is used to form an intermittent coating layer on the base material sheet 304, one side at a time. It is difficult, after completing the process of applying a first coating layer 320 on one side, to set a second coating layer 320 on the other side in an accurate relative position with the first coating layer 320. An attempt to accomplish a highly accurate relative positioning increases the cost of the mold.
Another problem of the coating die 400 lies in that when the coating material 302 is stopped from being supplied as the coating die 400 comes away from the base material sheet 304, the coating material 302 causes drips 400a (FIG. 3B), which in turn causes a bulge 320a at the starting end on the occasion of resuming the coating job (FIG. 3C). As a consequence, the thickness of the coating layer 320 undergoes a variation, thereby leading to a deteriorated thickness accuracy.